The present invention relates generally to a process for the preparation of substituted bis-ethers. More particularly, the present invention relates to an aqueous process for preparing substituted bis-ethers such as .alpha.,.omega.-bis-(4-aminophenoxy)-alkyls. The substituted bis-ethers are useful as precursors in preparing a variety of polymers or polymer precursors, such as polyimines, polyisocyanates and the like. These polymers and polymer precursors can, in turn, be used in preparing other polymer products such as polyether imides, polyamide-ethers, polyurethanes, polyureas and the like.
Known methods for preparing diamine substituted bis-ethers are generally complex. In fact, one method used to prepare water insoluble diamines of the formula ##STR1## wherein A is a divalent alkyl radical of up to about eighteen carbon atoms, involves seven steps. In a first step, acetamidophenol is added, with stirring, to dimethylformamide to form a mixture. Stirring of the mixture is continued through step three of the method. In step two, potassium carbonate and a dihaloalkane are added to the mixture after the amidophenol dissolves. In a third step, the mixture is heated under a nitrogen purge at reflux for four hours. In a fourth step, stirring is stopped and the mixture is poured into ice water and allowed to stand for several hours to precipitate a diamide. Fifth, the precipitate is filtered, washed with water and dried. Sixth, the diamide precipitate is hydrolyzed with an acid and alcohol mixture to provide a diamine salt. Finally, the diamine salt is isolated and then slurried with a saturated aqueous NaHCO.sub.3 solution to neutralize the salt and yield free diamine.
The aforementioned known process suffers from two primary disadvantages from an industrial process viewpoint. First, the yield is comparatively low--only about fifty percent under optimal conditions. Second, the process is complex and involves at least one intermediate drying step and a final alcohol recovery process. These disadvantages translate to significant cost and equipment constraints which make the process economically unattractive.
A process for preparing diamines with yields in excess of seventy percent, based upon starting materials, would be desirable. A simple, single vessel method wherein intermediate isolation and purification steps are eliminated would also be desirable.